Theta Laser

Abstract

An unidirectional short-wave infrared fiber laser, comprising a theta cavity, with a gain unit based on rare-earth cations-doped fiber, the theta cavity having a ring cavity with two additional 2 input ports×2 output ports directional couplers DC 1 and DC 2 inserted therein, one port of the directional coupler DC 1 connected to another port of the directional coupler DC 2 , forming an S-shaped feedback; a band-pass filter to select at a laser wavelength by filtering through transmission inside the theta cavity, the band-pass filter is one of the list comprising a grating-based filter, a Fabry-Perot etalon, and a phase shifted fiber-Bragg grating; and a reflective fiber Bragg grating (FBG) to select the laser wavelength by filtering through reflection inside the theta cavity, the Bragg grating is a notch filter, and the fiber Bragg grating (FBG) is attached to an unused port of the directional coupler DC 1 or DC 2.

1 - 11 . (canceled) 
     
     
         12 : A unidirectional short-wave infrared fiber laser comprising:
 a theta cavity with a gain unit based on rare-earth cations-doped fiber, the theta cavity including a ring cavity with two additional 2 input ports×2 output ports directional couplers DC 1  and DC 2 , one port of the directional coupler DC 1  being connected to another port of the directional coupler DC 2 , forming an S-shaped feedback;   a band-pass filter configured to select at a laser wavelength by filtering through transmission inside the theta cavity, the band-pass filter includes at least one of a grating-based filter, a Fabry-Perot etalon, and a phase shifted fiber-Bragg grating; and   a reflective fiber Bragg grating (FBG) configured to select the laser wavelength by filtering through reflection inside the theta cavity,   wherein the fiber Bragg grating (FBG) is a notch filter, and   wherein the fiber Bragg grating (FBG) is attached to an unused port of the directional coupler DC 1  or DC 2 .   
     
     
         13 : The fiber laser of  claim 12 , wherein the rare-earth cation-doped fiber includes at least one of a thulium-doped silica fiber for emission at 1700-2100 nm, a holmium-doped silica fiber for emission at 2000-2150 nm, thulium-holmium-co-doped silica fibers for emission at 1800-2150 nm, a thulium-doped fluoride fiber for emission at 2200-2500 nm, a holmium-doped fluoride fiber for emission around 3000 nm, and an erbium-doped fluoride fiber for emission around 2800 nm and 3500 nm. 
     
     
         14 : The fiber laser of  claim 12 , wherein the theta cavity with fiber Bragg grating is a truly all-fiber configuration without packaged free-space elements. 
     
     
         15 : The fiber laser of  claim 12 , wherein the rare-earth cation-doped fiber is configured to exhibit the Kerr-nonlinearity coefficient higher than corresponding nonlinear coefficients of a passive fibers in the cavity and to include a nonlinear amplifying loop mirror (NALM), including a cation-doped fiber, and the S-shaped feedback. 
     
     
         16 : The fiber laser of  claim 12 , further comprising:
 a solid-state saturable absorber (SESAM) attached to one of the unused ports of the couplers DC 1  or DC 2 , to achieve a pulsed operation of the theta cavity.   
     
     
         17 : The fiber laser of  claim 12 , further comprising:
 an optimized nonlinear amplifying loop mirror (NALM) acting as an artificial saturable absorber, to achieve a pulsed operation of the theta cavity.   
     
     
         18 : The fiber laser of  claim 16 , further comprising:
 a section of dispersion compensating fiber to reduce a duration of generated pulses of the pulsed operation.   
     
     
         19 : The fiber laser of  claim 17 , further comprising:
 a section of dispersion compensating fiber to reduce a duration of generated pulses of the pulsed operation.   
     
     
         20 : The fiber laser of  claim 12 , further comprising at least one of a polarization controller, and a polarizer in the cavity, thereby achieving an enhanced functionality. 
     
     
         21 : The fiber laser of  claim 12 , wherein the theta cavity with fiber Bragg grating is configured to operate at two different wavelengths, by two fiber Bragg gratings attached to free ports of directional couplers DC 1  and DC 2 , or fiber Bragg gratings cascaded at one port, to emit at a same laser transition. 
     
     
         22 : The fiber laser of  claim 12 , wherein the theta cavity with fiber Bragg grating is configured to operate at two different wavelengths, comprising two fiber Bragg gratings attached to free ports of directional couplers DC 1  and DC 2 , or fiber Bragg gratings cascaded at one port, emitting at different laser transitions of a single or dual gain units.